Alerting php when new event occurs in linux debian - php

Question

I have a daemon program that prints in the terminal when new device is plugged or removed, now i want it to be printed in php like the way it was printed in linux. it's like realtime output. when a new device is plugged in linux it will alert php without you clicking any button it just prints in the screen. what my daemon program prints in linux also php prints.
I also have another program which scan devices but not daemon i can get it's output without a problem and prints it in php.
How am i supposed to make a real time output with my daemon program in php?
Thanks,

Answer 1

Comments becoming long so I add a post here.
First off the redirection of stderr and stdout to file by ~$ my-daemon >> my_logfile 2>&1 - unless your daemon has a log-file option.
Then you could perhaps use inotifywait with the -m flag on modify events (if you want to parse/do something on system outside PHP, i.e. by bash.)
Inotify can give you notification on various changes - This is i..e a short few lines of a bash script I use to check for new files in a specific directory:
notify()
{
...
inotifywait -m -e moved_to --format "%f" "$path_mon" 2>&- |
awk ' { print $0; fflush() }' |
while read buf; do
printf "NEW:[file]: %s\n" "$buf" >> "$file_noti_log"
blah blah blah
...
done
}
What this does is: each time a file get moved to $path_mon the script enters inside the while loop and perform various actions defined by the script.
Haven't used inotify on PHP but this looks perhaps like what you want:
inotify_init (separate module in PHP).
inotify check various events in one or several directories, or you can target a specific file. Check man inotifywait or inotify. You would most likely want to use the "modify" flag, "IN_MODIFY" under PHP: Inotify Constants.
You could also write your own in C. Haven't read this page, but IBM's pages use to be quite OK : Monitor file system activity with inotify
Another option could be to use PCNTL or similar under PHP.

Answer 2

it will alert php without you clicking any button
So you're talking about client side PHP.
The big problem is alerting the client browser.
For short lengths of time you could ignore the problem and just disable all buffering and send the daemon output to the browser. It's neither elegant nor really working in the long run, and it has... aesthetic issues. Moreover, you can't really manipulate the output client side at all, not easily or cleanly at least.
So you need to have a program running on the client, which means Javascript. The JS and the PHP programs must communicate, and PHP must also talk to the daemon, or at least monitor what it's doing.
There are ways of doing the first using Web Sockets, or maybe multipart-x-mixed-replace, but they're not very portable yet.
You could refresh the Web page but that's wasteful, and slow.
The problem of getting the notification to the client browser is then, in my opinion, best solved with an AJAX poll. You don't get an immediate alert, but you do get alerted within seconds.
You would send a query to PHP from AJAX every, say, 10 seconds (10000 ms)
function poll_devices() {
$.ajax({
url: '/json/poll-devices.php',
dataType: 'json',
error: function(data) {
// ...
},
success: function(packet) {
setTimeout(function() { poll_devices(); }, 10000);
// Display packet information
},
contentType: 'application/json'
});
}
and the PHP would check the accumulating log and send the situation.
Another possibility is to have the PHP script block up to 20 seconds, not enough to make AJAX time out and give up, and immediately return in case of changes. You would then employ an asynchronous AJAX function to drive the poll back-to-back.
This way, the asynchronous function starts and immediately goes to sleep while the PHP script is sleeping too. After 20 seconds, the call returns and is immediately re-issued, sleeping again.
The net effect is to keep one connection constantly open, and changes being echoed back to client side Javascript immediately. You have to manage connection interruptions, though. But this way, every 20 seconds you only issue one call, and still manage to be alerted almost instantly.
Server side PHP can check the log file's size at the start (last read position being saved in the session), and keep it open read only in shared mode and block reads with fgets(), if the daemon allows it.
Or you could pipe the daemon to logger, and get messages to syslog. Configure syslog to send those messages to a specific unbuffered file readable by PHP. Now PHP should be able to do everything with fopen(), ftell() and fgets(), without requiring additional notification systems.